System and process for low-temperature circulating drying of municipal sludge and emission reduction of dry gas

Abstract

The invention relates to a system and a process for low-temperature circulating drying of municipal sludge and emission reduction of dry gas. The system comprises a sunlight room, an absorption device, a catalysis device, a heat exchanger, a circulating fan, a condenser and a heater, the sunlight room is kept closed, a weakly alkaline solution is stored in the absorption device, a catalyst capable of purifying peculiar smell gas is stored in the catalysis device, and a gas outlet of the sunlight room communicates with a heat exchange inlet of the heat exchanger; a heat exchange outlet of the heat exchanger is communicated with an air inlet of the absorption device, an air outlet of the absorption device is communicated with an inlet of the condenser through the circulating fan, an outlet of the condenser is communicated with an air inlet of the catalytic device, and an air outlet of the catalytic device is communicated with the atmosphere and a medium inlet of the heat exchanger. A medium outlet of the heat exchanger communicates with an air inlet of the sunlight room through the heater. The system not only is energy-saving and environment-friendly, but also can promote the cyclic utilization of sludge resources.

Description

Technical Field

[0001] This invention relates to the field of energy conservation and environmental protection technology, and in particular to a system for low-temperature circulating drying of urban sludge and emission reduction of drying gas, as well as a process for low-temperature circulating drying of urban sludge and emission reduction of drying gas using this system. Background Technology

[0002] Urban sludge refers to the sediment produced during urban wastewater treatment, primarily originating from primary sedimentation tanks, secondary sedimentation tanks, and sludge thickening tanks in urban wastewater treatment plants. In recent years, with the acceleration of urbanization and the improvement of wastewater treatment facilities, the amount of urban sludge generated has increased rapidly. Statistics show that treating 10,000 tons of wastewater produces 1.5 to 2 tons of sludge, and my country's annual urban sludge production has reached tens of millions of tons. Because urban sludge contains large amounts of organic matter, heavy metals, pathogenic microorganisms, and parasite eggs, it poses a serious threat to the environment and human health if not properly treated and disposed of.

[0003] Currently, in the treatment of urban sludge, the commonly used thermal drying technology (such as air drying and rotary kiln drying) not only requires a large amount of energy to provide heat, but also causes irreversible damage to the microorganisms and organic matter in the sludge, and produces a large amount of malodorous gases and other harmful gases. In addition, due to the long-term exposure to high temperature and high humidity, the equipment of thermal drying technology is also easily corroded and requires frequent maintenance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an energy-saving and environmentally friendly system for low-temperature circulating drying of urban sludge and emission reduction of drying gas, which promotes the recycling of sludge resources.

[0005] The present invention adopts the following technical solution:

[0006] This invention provides a system for low-temperature circulating drying of urban sludge and emission reduction of drying gas, including a sunroom, an absorption device, a catalytic device, a heat exchanger, a circulating fan, a condenser, and a heater. The sunroom is kept sealed. The absorption device contains a weakly alkaline solution, and the catalytic device contains a catalyst capable of purifying odorous gases. The outlet of the sunroom is connected to the heat exchange inlet of the heat exchanger, and the heat exchange outlet of the heat exchanger is connected to the inlet of the absorption device. The outlet of the absorption device is connected to the inlet of the condenser through the circulating fan, and the outlet of the condenser is connected to the inlet of the catalytic device. The outlet of the catalytic device is simultaneously connected to the atmosphere and the medium inlet of the heat exchanger. The medium outlet of the heat exchanger is connected to the inlet of the sunroom through the heater.

[0007] Preferably, the interior space of the sunroom is divided into multiple sealed drying zones. The air outlet of each drying zone is connected to the heat exchange inlet of the heat exchanger, and the air inlet of each drying zone is connected to the heater through a return pipe. Each return pipe is equipped with an on / off valve.

[0008] Preferably, the absorption device has an air inlet at the lower end and an air outlet at the upper end, and a weak alkaline solution is continuously sprayed from the top to the bottom inside the absorption device.

[0009] Preferably, the weakly alkaline solution in the absorption device is a sodium hydroxide solution, ammonia water, or a mixed solution of sodium hydroxide and calcium nitrate.

[0010] Preferably, the catalytic device includes a cylindrical body and a catalytic unit. The cylindrical body has an air inlet around its periphery and an air outlet at its upper end. The catalytic unit is located inside the cylindrical body and contains a catalyst. The air inlet is connected to the air outlet through the catalytic unit.

[0011] Preferably, the catalytic unit is a spiral guide air duct with a catalyst bed installed inside, and the catalyst bed is deployed with catalyst.

[0012] Preferably, the catalyst bed is equipped with an ultraviolet device for providing photovoltaic activation energy, and the catalyst on the catalyst bed is a composite catalyst, which includes the following raw materials in parts by weight: 800-850 parts activated carbon, 50-70 parts titanium dioxide, 30-50 parts zinc oxide, 3-5 parts platinum, 3-5 parts palladium, 15-25 parts copper oxide and 10-20 parts manganese oxide.

[0013] Preferably, the catalytic device further includes a sensor and a central control unit. The sensor is installed in the catalytic unit and can monitor the composition and concentration of the gas in real time. The central control unit is simultaneously connected to the sensor, the ultraviolet device, and the circulating fan.

[0014] Preferably, the condenser is connected to the chilled water circulation system of the industrial refrigeration unit, and the gas entering the condenser exchanges heat with the chilled water circulation system to achieve cooling and condensation.

[0015] This invention also provides a process for low-temperature circulating drying of municipal sludge and emission reduction of drying gas, employing any of the above-mentioned systems for low-temperature circulating drying of municipal sludge and emission reduction of drying gas, and including the following steps:

[0016] S1: Add urban sludge into a sunroom, use solar energy to dry and dehumidify the sludge, and enrich odor and moisture to form a mixed odor and moisture gas.

[0017] S2: The odorous and humid mixed gas enters the heat exchanger under the influence of the dry hot air blown into the sunroom to exchange heat with the purified gas for cooling and dehumidification. Then it is passed into the absorption device, where the weak alkaline solution absorbs the acidic gas in the odorous and humid mixed gas and degrades the toxic gas in it, thus obtaining deacidified gas.

[0018] S3: The deacidified gas is passed into the condenser for cooling and condensation by the action of the circulating fan, and then passed into the catalytic device to obtain purified gas under the action of the catalyst. Part of the purified gas is diverted and discharged to the atmosphere, and the other part of the purified gas enters the heat exchanger to mix with the odorous and moist gas to heat up and dehumidify, thus obtaining dehumidified gas.

[0019] S4: The dehumidified gas continues to be fed into the heater to be heated and reheated to form dry hot gas. The dry hot gas is then fed into the sunroom to carry away the odorous and moist mixed gas into the next treatment cycle.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In the urban sludge low-temperature circulating drying and drying gas emission reduction system of the present invention, the various parts are connected in sequence to form a circulating system. In the sunroom, sunlight is used as a heat source to dry the urban sludge at low temperature and generate a mixture of odorous and moist gas. The mixture of odorous and moist gas first passes through a heat exchanger for cooling and dehumidification treatment, and then passes through an absorption device to remove acidic and toxic gases. Then it passes through a catalytic device for catalytic purification to form purified gas that can be discharged into the atmosphere. Only a portion of the purified gas is directly discharged, while the other portion passes through a heat exchanger and a heater and is reused in the sunroom.

[0022] Obviously, the urban sludge low-temperature circulating drying and drying gas emission reduction system of the present invention adopts low-temperature drying technology with solar thermal source. The entire drying process is completed in an environment below 60°C, thereby effectively preserving the organic matter and nutrients in the sludge, making it suitable for subsequent resource utilization, such as composting and soil improvement, and promoting the reuse of sludge resources and the development of circular economy. In addition, the urban sludge low-temperature circulating drying and drying gas emission reduction system of the present invention diverts part of the purified gas for emission and recycles the other part. The recycled gas participates in the drying process again, reducing exhaust gas emissions and environmental pollution, and realizing the efficient utilization and recycling of gas resources.

[0023] The process for low-temperature circulating drying of urban sludge and emission reduction of drying gas in this invention adopts the above-mentioned system, and naturally has the above-mentioned beneficial effects, which will not be elaborated here. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the system structure for low-temperature circulating drying of urban sludge and emission reduction of drying gas in an embodiment of the present invention.

[0025] The reference numerals in the attached figures are explained as follows:

[0026] 1. Sunroom; 6. Condenser

[0027] 101. Drying Zone 7. Heater

[0028] 2. Absorption device; 8. Return pipe

[0029] 3. Catalytic converter; 9. On / off valve

[0030] 4. Heat exchanger 10. Connecting pipe

[0031] 5. Circulating fan Detailed Implementation

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0035] Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0036] See Figure 1This embodiment provides a system for low-temperature circulating drying of urban sludge and emission reduction of drying gas, including a sunroom 1, an absorption device 2, a catalytic device 3, a heat exchanger 4, a circulating fan 5, a condenser 6, and a heater 7. The sunroom 1 is kept sealed. The absorption device 2 contains a weakly alkaline solution, and the catalytic device 3 contains a catalyst capable of purifying odorous gases. The outlet of the sunroom 1 is connected to the heat exchange inlet of the heat exchanger 4, and the heat exchange outlet of the heat exchanger 4 is connected to the inlet of the absorption device 2. The outlet of the absorption device 2 is connected to the inlet of the condenser 6 through the circulating fan 5, and the outlet of the condenser 6 is connected to the inlet of the catalytic device 3. The outlet of the catalytic device 3 is simultaneously connected to the atmosphere and the medium inlet of the heat exchanger 4. The medium outlet of the heat exchanger 4 is connected to the inlet of the sunroom 1 through the heater 7.

[0037] In this embodiment, the various parts of the urban sludge low-temperature circulating drying and drying gas emission reduction system are connected in sequence to form a circulating system. In the sunroom 1, sunlight is used as a heat source to dry the urban sludge at low temperature and generate a mixture of odorous and moist gas. The mixture of odorous and moist gas first passes through the heat exchanger 4 for cooling and dehumidification treatment, and then passes through the absorption device 2 to remove acidic and toxic gases. Then it passes through the catalytic device 3 for catalytic purification to form purified gas that can be discharged into the atmosphere. Only a part of the purified gas is directly discharged, and the other part enters the sunroom 1 again for reuse after passing through the heat exchanger 4 and the heater 7.

[0038] Obviously, the urban sludge low-temperature circulating drying and drying gas emission reduction system of this embodiment adopts low-temperature drying technology with solar thermal source. The entire drying process is completed in an environment below 60°C, thereby effectively preserving the organic matter and nutrients in the sludge, making it suitable for subsequent resource utilization, such as composting and soil improvement, and promoting the reuse of sludge resources and the development of circular economy. In addition, the urban sludge low-temperature circulating drying and drying gas emission reduction system of this embodiment diverts part of the purified gas for emission and recycles the other part. The recycled gas participates in the drying process again, reducing exhaust gas emissions and environmental pollution, and realizing the efficient utilization and recycling of gas resources.

[0039] Preferably, see Figure 1 The interior space of the sunroom 1 is divided into multiple sealed drying zones 101. The air outlet of each drying zone 101 is connected to the heat exchange inlet of the heat exchanger 4. The air inlet of each drying zone 101 is connected to the heater 7 through a return pipe 8, and each return pipe 8 is equipped with an on / off valve 9.

[0040] Sunroom 1 adopts a zoned drying strategy, with each drying zone 101 having a drying time of 2 hours. Different drying zones 101 are isolated and dried at regular intervals. While a certain drying zone 101 in sunroom 1 is undergoing low-temperature circulation treatment, the other drying zones 101 are sealed through the on / off valve 9. Natural heat sources such as sunlight are used to dry and dehumidify the urban sludge, and to enrich the odor and moisture. After the drying zone 101 has completed the low-temperature circulation treatment, the air passage is changed to sequentially perform low-temperature circulation treatment on other drying zones 101.

[0041] Preferably, the absorption device 2 has an air inlet at the lower end and an air outlet at the upper end, and a weak alkaline solution is continuously sprayed from top to bottom inside the absorption device 2. After the gas enters the absorption device 2 through the air inlet, it will move upward, thereby forming convection with the weak alkaline solution moving downward. The weak alkaline solution absorbs the acidic gas in the mixed gas and degrades some of the toxic gas.

[0042] Preferably, the weakly alkaline solution in the absorption device 2 is a sodium hydroxide solution, ammonia water, or a mixed solution of sodium hydroxide and calcium nitrate.

[0043] Preferably, the catalytic device 3 includes a cylindrical body and a catalytic unit. The cylindrical body has an air inlet around its perimeter and an air outlet at its upper end. The catalytic unit is disposed inside the cylindrical body and contains a catalyst. The air inlet is connected to the air outlet through the catalytic unit. After the gas enters the cylindrical body through the air inlet, it undergoes catalytic purification by contacting the catalyst in the catalytic unit before being discharged from the air outlet.

[0044] Better, see Figure 1 In this embodiment, the cylindrical body is provided with multiple air inlets around its periphery, and multiple catalytic units are provided inside the cylindrical body. The outlet of the condenser 6 is connected to multiple connecting pipes 10, and each connecting pipe 10 is connected to one of the air inlets of the cylindrical body in a corresponding manner. Each air inlet is connected to the outlet through an independent catalytic unit, thereby accelerating the catalytic purification efficiency of the catalytic device 3 on the gas.

[0045] Preferably, the catalytic unit is a spiral guide air duct with a catalyst bed installed inside, and the catalyst bed is deployed with catalyst.

[0046] The spiral-shaped airflow duct ensures that the introduced gas undergoes a full catalytic reaction process and effectively avoids problems such as airflow short-circuiting and incomplete contact. Specifically, the spiral-shaped airflow duct increases the specific surface area of ​​the introduced gas, allowing for a more thorough catalytic reaction. Furthermore, it allows for further sieving of the components in the introduced gas. Because different gas components will be distributed at different positions in the spiral airflow path due to their different densities under the influence of centrifugal force—for example, denser gases will tend to be concentrated in the outer layer—more rational catalyst deployment can be achieved in actual catalytic reactions, making the actual catalyst application more targeted.

[0047] Preferably, the catalyst bed is equipped with an ultraviolet device for providing photovoltaic activation energy, and the catalyst on the catalyst bed is a composite catalyst, which includes the following raw materials in parts by weight: 800-850 parts activated carbon, 50-70 parts titanium dioxide, 30-50 parts zinc oxide, 3-5 parts platinum, 3-5 parts palladium, 15-25 parts copper oxide and 10-20 parts manganese oxide.

[0048] It should be noted that in the composite catalyst, activated carbon serves as the catalyst support, while the remaining raw materials together constitute the catalyst. After the catalyst absorbs ultraviolet photons provided by the ultraviolet device, the energy of the photons excites electrons in the catalyst, causing the electrons to jump from the valence band to the conduction band to form electron-hole pairs. The photogenerated electrons and holes ultimately complete the reaction on the catalyst surface.

[0049] Preferably, in this embodiment, the ultraviolet device is mounted on the catalyst bed via a polymethyl methacrylate plate, and the catalyst bed adopts a modular design consisting of multiple catalyst sub-beds spliced ​​together, so that the catalyst bed is easy to replace and maintain.

[0050] Preferably, the catalytic device 3 also includes a sensor and a central control unit. The sensor is installed in the catalytic unit and can monitor the composition and concentration of the gas in real time. The central control unit is simultaneously connected to the sensor, the ultraviolet device and the circulating fan 5.

[0051] The catalytic device 3 monitors the composition and concentration of the gas in real time through sensors. After receiving the data collected by the sensors, the central control unit can automatically adjust the ultraviolet equipment to control the working status of the catalytic unit and control the air supply of the circulating fan 5 to ensure that the catalytic device 3 is always in the best operating condition.

[0052] Preferably, the condenser 6 is connected to the chilled water circulation system of the industrial refrigeration unit, and the gas entering the condenser 6 exchanges heat with the chilled water circulation system to cool and condense.

[0053] Condenser 6 cools and condenses the gas through a precisely controlled chilled water circulation system, which can rapidly cool the gas to 5-15℃. During the condensation process of condenser 6, not only is the gas temperature effectively reduced, but the gas humidity content is also reduced, which is beneficial to subsequent gas purification and catalytic processes, helps to improve the overall treatment efficiency, and effectively removes volatile organic compounds and other odor components from the gas, thereby ensuring that the treated gas meets strict environmental emission standards.

[0054] Furthermore, the following are several specific embodiments:

[0055] Example 1

[0056] In Example 1, the weakly alkaline solution in the absorption device 2 is a sodium hydroxide solution, and the composite catalyst on the catalyst bed includes the following raw materials by weight: 800g activated carbon, 50g titanium dioxide, 30g zinc oxide, 3g platinum, 3g palladium, 15g copper oxide, and 10g manganese oxide.

[0057] Example 2

[0058] In Example 2, the weakly alkaline solution in the absorption device 2 is ammonia water, and the composite catalyst on the catalyst bed includes the following raw materials by weight: 820g activated carbon, 60g titanium dioxide, 40g zinc oxide, 4g platinum, 4g palladium, 20g copper oxide, and 15g manganese oxide.

[0059] Example 3

[0060] In Example 3, the weakly alkaline solution in the absorption device 2 is a mixed solution of sodium hydroxide and calcium nitrate, and the composite catalyst on the catalyst bed includes the following raw materials by weight: 850g activated carbon, 70g titanium dioxide, 50g zinc oxide, 5g platinum, 5g palladium, 25g copper oxide, and 20g manganese oxide.

[0061] In particular, to confirm the actual performance of the urban sludge low-temperature circulating drying and drying gas emission reduction system of this application, the following performance tests were conducted:

[0062] 1. Energy consumption performance and odor removal effect test

[0063] Four samples of urban sludge were taken and named Sample A, Sample B, Sample C and Sample D respectively. The initial mass of each sample was 1 kg and the initial moisture content was 30%.

[0064] Under the same conditions, samples A and B were respectively sent to the urban sludge low-temperature circulating drying and drying gas emission reduction system of Example 1 for drying and odor treatment, and samples C and D were respectively sent to the hot air drying system (existing technology) for drying and odor treatment. The initial air volume was 600 L / min, and the volume ratio of the drying gas discharged from the system to the drying gas circulating into the air path was 1:9.

[0065] During the experiment, the water content of each sample was continuously recorded, as well as the time and energy consumed when the water content of each sample dropped to 10%. At the same time, the gas discharged from the system was detected and recorded. The results are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] As shown in Table 1, when using the system of low-temperature circulating drying and drying gas emission reduction of urban sludge in Example 1 for sludge drying, it can effectively reduce drying energy consumption while improving the removal of odor content emitted by sludge, and the time spent is almost the same as that of hot air drying system.

[0070] 2. Soil biological activity test

[0071] After the drying and odor treatment tests of each sample in the "Energy Consumption Performance and Odor Removal Effect Test" were completed, topsoil of the sample soil was collected and DNA was extracted. The concentration and purity of the extracted DNA were measured and diluted to 20 ng / uL with sterile water.

[0072] Then, each sample was analyzed using PCR. The qPCR reaction system included 10 μL SYBR Green Supermix reagent, 0.4 μL forward primer (10 μM), 0.4 μL reverse primer (10 μM), 2 μL template DNA (20 ng / μL), and 7.2 μL sterile pure water. The qPCR reaction process was as follows: 1. Pre-denaturation: heat to 95°C for 5 minutes; 2. Denaturation: heat to 95°C for 15 seconds; 3. Annealing: cool to 60°C for 30 seconds; 4. Extension: heat to 72°C for 30 seconds; and a total of 40 cycles were performed.

[0073] Subsequently, the Ct values ​​were analyzed using qPCR instrument software, and the number of bacteria in the samples was calculated based on the standard curve. The final results are recorded in Table 2.

[0074] Table 2

[0075] Sample number Ct value of methanogenic archaea Methanogenic archaea concentration (copy number / g sludge) Sample A 24 7.2E+04 Sample B 23.4 7.2E+04 Sample C 19.2 1.1E+03 Sample D 19.5 6.3E+02

[0076] As shown in Table 2, because the system for low-temperature circulating drying of urban sludge and emission reduction of drying gas in Example 1 is carried out at a relatively low temperature, it can better preserve the biodiversity in the soil, which is beneficial for subsequent sludge treatment and resource utilization.

[0077] This embodiment also provides a process for low-temperature circulating drying of urban sludge and reduction of drying gas emissions, see [link to relevant documentation]. Figure 1 The system employing the aforementioned low-temperature circulating drying of urban sludge and the reduction of drying gas emissions includes the following steps:

[0078] S1: Add urban sludge into sunroom 1, and use solar energy to dry and dehumidify the sludge, thereby enriching odor and moisture to form a mixed odor and moisture gas.

[0079] S2: The odorous and humid mixed gas enters the heat exchanger 4 under the influence of the dry hot air blown into the sunroom 1 to exchange heat with the purified gas for cooling and dehumidification treatment. Then it is passed into the absorption device 2, where the weak alkaline solution absorbs the acidic gas in the odorous and humid mixed gas and degrades the toxic gas in it, thereby obtaining the deacidified gas.

[0080] S3: The deacidified gas is passed into the condenser 6 for cooling and condensation under the action of the circulating fan 5, and then passed into the catalytic device 3 to obtain purified gas under the action of the catalyst. Part of the purified gas is diverted and discharged to the atmosphere, and the other part of the purified gas enters the heat exchanger 4 to heat up and dehumidify the mixed gas of odor and moisture to obtain dehumidified gas.

[0081] S4: The dehumidified gas continues to be fed into heater 7 to be heated and reheated to form dry hot gas. The dry hot gas is then fed into sunroom 1 to carry away the odorous and moist mixed gas into the next treatment cycle.

[0082] The process of low-temperature circulating drying of urban sludge and emission reduction of drying gas in this embodiment combines low-temperature circulating drying of urban sludge and emission reduction of drying gas. It not only improves the efficiency of sludge drying, but also significantly reduces the energy consumption of the production process and lowers the operating cost. Compared with traditional sludge drying and odor treatment, it is more energy-efficient and provides an efficient and environmentally friendly solution for urban environmental governance. It has good economic benefits and prospects for promotion and application.

[0083] It should be noted that heat exchanger 4 achieves the cooling of the odorous and moist mixed gas and the preheating of the purified gas through heat exchange between the odorous and moist mixed gas and the purified gas, thereby better realizing the subsequent drying and catalytic deodorization steps of the two gases. While reducing system energy consumption, it also provides a more suitable ambient temperature for the subsequent catalytic reaction.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions, characterized in that: The invention comprises a sun room (1), an absorption device (2), a catalytic device (3), a heat exchanger (4), a circulating fan (5), a condenser (6) and a heater (7). The sun room (1) is kept airtight. A weak alkaline solution is stored inside the absorption device (2). A catalyst capable of purifying odorous gas is stored inside the catalytic device (3). The air outlet of the sun room (1) is connected to the heat exchange inlet of the heat exchanger (4). The heat exchange outlet of the heat exchanger (4) is connected to the air inlet of the absorption device (2). The air outlet of the absorption device (2) is connected to the inlet of the condenser (6) through the circulating fan (5). The outlet of the condenser (6) is connected to the air inlet of the catalytic device (3). The air outlet of the catalytic device (3) is connected to the atmosphere and the medium inlet of the heat exchanger (4) at the same time. The medium outlet of the heat exchanger (4) is connected to the air inlet of the sun room (1) through the heater (7).

2. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 1, characterized in that: The internal space of the sun room (1) is partitioned into a plurality of sealed drying partitions (101), the air outlet of each drying partition (101) is connected to the heat exchange inlet of the heat exchanger (4), the air inlet of each drying partition (101) is connected to the heater (7) via a return pipe (8), and each return pipe (8) is provided with an opening and closing valve (9).

3. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 1, characterized in that: The lower end of the absorption device (2) is provided with an air inlet, and the upper end is provided with an air outlet, and a weak alkaline solution is continuously sprayed in the absorption device (2) from the top to the bottom.

4. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 1, characterized in that: The weak alkaline solution in the absorption device (2) is a sodium hydroxide solution, ammonia water or a mixed solution of sodium hydroxide and calcium nitrate.

5. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 1, characterized in that: The catalytic device (3) comprises a cylindrical body and a catalytic unit. The cylindrical body is provided with an air inlet around its periphery and an air outlet at its upper end. The catalytic unit is arranged inside the cylindrical body and contains a catalyst. The air inlet is connected to the air outlet through the catalytic unit.

6. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 5, characterized in that: The catalytic unit is a spiral guide air duct with a catalyst bed detachably installed inside, and a catalyst is arranged on the catalyst bed.

7. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 6, characterized in that: The catalyst bed is equipped with an ultraviolet device for providing photovoltaic activation energy, and the catalyst on the catalyst bed is a composite catalyst, which includes the following raw materials in parts by weight: 800-850 parts of activated carbon, 50-70 parts of titanium dioxide, 30-50 parts of zinc oxide, 3-5 parts of platinum, 3-5 parts of palladium, 15-25 parts of copper oxide and 10-20 parts of manganese oxide.

8. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 7, characterized in that: The catalytic device (3) also includes a sensor and a central control unit. The sensor is arranged in the catalytic unit and can monitor the composition and concentration of the gas in real time. The central control unit is simultaneously connected to the sensor, the ultraviolet device and the circulating fan (5) by signal.

9. The system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to claim 1, characterized in that: The condenser (6) is connected to a chilled water circulation system on an industrial refrigeration unit, and the gas entering the condenser (6) exchanges heat with the chilled water circulation system to cool down and condense.

10. A process for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions, characterized in that: A system for low-temperature circulation drying of municipal sludge and reduction of drying gas emissions according to any one of claims 1 to 9 is used, and comprises the following steps: S1: adding municipal sludge into the sun room (1), drying and dehumidifying the sludge by solar energy, and enriching the odor and moisture to form a mixed gas of odor and moisture; S2: The odor-humidity mixed gas is driven by the dry hot air blown into the sun room (1) to enter the heat exchanger (4) to exchange heat with the purified gas for cooling and dehumidification, and then enters the absorption device (2). The weak alkaline solution in the absorption device (2) absorbs the acidic gas in the odor-humidity mixed gas and degrades the toxic gas therein, thereby obtaining deacidified gas; S3: The deacidified gas is passed into the condenser (6) under the action of the circulating fan (5) to be cooled and condensed, and then passed into the catalytic device (3) to obtain purified gas under the action of the catalyst. A part of the purified gas is discharged into the atmosphere, and the other part of the purified gas enters the heat exchanger (4) to heat and dehumidify the mixed gas with the odor and moisture to obtain dehumidified gas; S4: The dehumidified gas continues to be introduced into the heater (7) to be heated and reheated to form dry hot gas, which is then introduced into the sun room (1) to carry away the odorous and moist mixed gas and enter the next treatment cycle.

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